1. Field of the Invention
This invention relates to an improved method of manufacturing semiconductor devices and, more specifically, it relates to a method of forming a single crystal film of a semiconductor on a substrate such as a dielectric material and then forming one or more devices, such as transistors, on the film.
2. Description of the Prior Art
For increasing the operational speed and packing density of semiconductor devices, attempts have been made to manufacture a semiconductor integrated circuit with a low stray capacitance by isolating circuit devices with dielectric material, and attempts have been made as well to laminate the circuit devices vertically and horizontally, that is, to manufacture a so-called three-dimensional integrated circuit. One well known method includes forming a semiconductor layer on a dielectric material and then forming circuit devices in the semiconductor crystalline layer. Such a semiconductor crystalline layer can be formed by depositing a non-single crystal semiconductor layer, such as a polycrystalline or amorphous semiconductor layer, on a substrate such as a dielectric material and irradiating the semiconductor layer with energy rays or beams such as laser beams or electron beams to heat the surface layer to cause recrystallization.
Referring to FIGS. 2a and 2b, there is shown a composite body of a semiconductor crystalline layer formed on a dielectric substrate in accordance with the conventional method as set forth above. In FIGS. 2a and 2b, there is shown a single crystal silicon substrate 11, a silicon oxide film 12, a polycrystalline silicon film 13 and a silicon nitride film 14 deposited on the polycrystalline film 13 and patterned as parallel stripes each of about 5 .mu.m in width and spaced apart at about 10 .mu.m intervals. The silicon oxide film 12 is formed by a thermal oxidation process, and the polycrystalline silicon film 13 and the silicon nitride film 14 are formed by a chemical vapor deposition process (hereinafter simply referred to as a "CVD" process). The polycrystalline silicon film 13 can be melted and recrystallized, for example, by irradiating the film with argon laser beams of about 100 .mu.m diameter scanning in parallel with the stripes of the silicon nitride film 14 at a rate of about 25 cm/sec. In this case, since the silicon nitride film 14 serves as an antireflection layer for the argon laser beam, the beam is more fully absorbed and the temperature of the polycrystalline silicon film 13 under such silicon nitride film portions 14 is therefore higher than that of the polycrystalline silicon film 13 in the regions where the silicon nitride film 14 is absent and where less energy is therefore absorbed by the film. The solidification and recrystallization of the polycrystalline film 13 begins and propagates continuously from the lower temperature regions with no silicon nitride film 14 toward the higher temperature regions of the polycrystalline silicon film 13 under the stripes of the silicon nitride film 14 to form single crystal structures.
Since in the conventional method just described, the radiation from the energy beam impinges directly on the semiconductor layer in which devices such as transistors are to be formed subsequently, power fluctuations, and other variations in the energy beam, even with relatively constant power, result in grain boundaries, unevenness and other defects in the single crystal structure so formed.